The statements in this section merely provide background information related to the present invention and may or may not constitute prior art.
A typical automatic transmission includes a hydraulic control system that, among other functions, is employed to actuate a plurality of torque transmitting devices. These torque transmitting devices may be, for example, friction clutches and brakes. The conventional hydraulic control system typically includes a main pump that provides a pressurized fluid, such as oil, to a plurality of valves and solenoids within a valve body. The main pump is driven by the engine or electric motor of the motor vehicle. The valves and solenoids are operable to direct the pressurized hydraulic fluid through a hydraulic fluid circuit to the plurality of torque transmitting devices within the transmission. The pressurized hydraulic fluid delivered to the torque transmitting devices is used to engage or disengage the devices in order to obtain different gear ratios.
In certain transmission configurations, actuation of the torque transmitting devices is achieved by selective release of an accumulator charged with hydraulic fluid. The accumulator is charged intermittently by the main pump and the main pump is typically deactivated when not charging the accumulator. However, during a vehicle start when the accumulator is empty, there is a delay in the operation of the hydraulic control system as the pump first charges the accumulator before the accumulator can supply pressurized hydraulic fluid to the hydraulic control system. Therefore, there is room in the art for a system to reduce or eliminate the shifting lag time due to charging the accumulator during a vehicle start.